Automatic interrupter for broadcast receivers



Sept. 22, 1936. R. D. wlcHMAN. JR.. ET Al. 2,055,164

AUTOMATIC INTERRUPTER FOR BROADCAST RECEIVERS Filed Deo. 14, 1932 ".5 ,waak

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Pon/ER aap/Ly c//eca/r 'fT T r lll/f 4 ATTORNEY Patented Sept. 22, 1936 1; UNITED STATES PATENT oFFleE AUTOMATIC INTERRUPTER FOR BROADCAST RECEIVERS Application December 14, 1932, serial No. 647,256

s claims. (c1. 25o-2o) .This invention relates to an automaticfinter-` a different frequency automatically to block the "electron iiow inthe radio frequency `tubes of the said conventional receiving set, whereby whena signal is received ofV the predetermined Y frequency to which the interrupter unit is responsive it is made audible While the initial signal 'is blocked, but upon cessation of such signal the initial signal will `again be rendered audible; all as will be described more fullyhereinafter.

It is an object of our invention to provide a xreceiving set Vfor signalsV of `different frequencies and so arranged that when signals .of `a predetermined frequency are received the reception of other Signals is automatically blocked and such audible reception is automatically resumed `upon cessation of the signals of such predeter- `mined frequency.

Another obj ectis to provide `an interrupter unit which .can be compactly housed Within .the cabinet of any conventional receiving set, and which utilizes the incoming signal-of a frequency different from that to which the conventional re ceiving set is tuned for automatically rendering audible the signal of predetermined different fre-` quency and simultaneously blocking the broadcast signalsV as received on `the conventional receiving set, while automatically permitting such 1 broadcast signals to resume to produce audible sounds when the predetermined` different frey quency signals have ceased.

Referring to the drawing wherein is shown in diagram a circuit embodying our invention:

The variable condenser C1 acting as a high frequency blocking condenser and in conjunction with the radio frequency choke L1, blocks type alternating current variable mu radio frequency pentode tube. Y

R1 is avariable resistor, the portion of which to the left of the slider is by-passed by a `fixed condenser C3 for adjusting the bias` on T1 to 5` give the Vcorrect volume when the interrupter unit is operating through the audio system of the receiving set. R2 is a resistor which acts as a bleeder between R3 and R1. R3 is a voltage drop.- resistor between the plate lead and screen grid lead for the screen grid potential. l C4 is a fixed by-pass condenser for the screenlgrid lead.

The tube T1 amplii'les the received signal which,- upon passing through the plate lead to the radio frequency coil L2 is again .tuned by a variable condenser C2 to obtain greater amplification, and upon passing through the voltage blocking-condenser C7 is impressed upon the grid of tube T2, a type 56 alternating current detector and amplifier. C5V is a fixed by-pass `and voltage blocking condenser for the plate lead of tube T1. l

The tubeT2 is arranged to act as a detector, and the resistor R7 and xed by-pass condenser C'I give the necessary bias. The resistor R8 is a grid-to-ground bleeder. l The tube T2 changes the signal from radio frequency to audio frequency and passing through the plate lead P it-is connected with .the plate lead of the rst audio stage in the conventional receiving set as at P to befurther amplified. Such connection is the same for a resistance coupled rst audio stage receiver of conventional circuit.

A radio frequency choke L3 with a fixed bypass condenser C9 in the plate lead of tube T2 servesto prevent radio frequency signals from going vthrough to the audio amplifiers.

When a signal is being received by the interrupter unit receiver the following change occurs. Tube T1 amplies the incoming signal and impresses this amplified incoming signal upon the detector of the said receiver` circuit. This amplied signal also comes through condenser Cs to the grid of tube T3, the signal acting as an applied voltage, alternating in character. Thus tube T3 acts as a rectifier.- During the positive half of each cycle of alternation, the plate of tube Ts will draw current, and during each negative halfcycle the tube T3 will not pass current. The resistor R5 is adjusted to such a value that it will not permit excessive current to flow from the 0 plate of tube T3 to the ground (chassis). The

with reference to the cathodes of the same tubes at the time the signal is received on the other receiving set, due to the rectified voltage output from tube T3. The said outputrwill tend to cut off the plate current fromV the radio frequency. tubes in the conventional receiving set.,V The tube Y characteristic of such tubes is completely changed by this and all amplification in .the conventional receiving set will cease. Y

This same output current from tube T1 flowing through the detector of its receiver or interrupter-- unit will change this signal, initially'ofrthe f re/ quency to which the interrupter unit istuned,V

from radio frequency to audio frequency, due to the action'of the detector tube T2,V and the inf" terrupter unit, being connected in the usual mannerto the rst audio transformer of the conventional broadcast receiver, the signal is amplifled and ultimately changed to soundin the usual way. During this time there is no interference from the signal venergy of the conventional reany. other alternating voltage.

ceiver. The resistor R4 is a limiting resistor to hold the output of tube T3 to a predetermined value.

. The alternating current voltage impressed upon the grid of tube T3, of course, initially is of radio frequency which becomes rectified the same as The rectied or directcurrent voltage from the plate of T3 is Yconveyedthrough the resistor Re to the low'potential end of the tuning coil or coils in the said conventional radio receiving set.

of T3 to the chassis or ground of the conventional radio receiver. YIts'purpose is to avoid a direct short circuit of any current flowing from the plate oftube T3 and also to permit the tubes of the conventional radio receiving set to operate with their customary grid bias whenever no signal is passing through the Vinterrupter unit.V

When a signal is received through the interrupter unit the rectifyingV action of tube T3, is established immediately and when suchlsignal ceases the rectification also, stops at once.

vThe tube T3 which is thus used as a control tube, is preferably ofthe same type as tube T2. The plate or anode of tube T1 is connected to the grid of tube T3 through the coupling condenser Cs. When a signal is passing through the tuned circuit ofthe interrupter unit, vsaid signal produces ay small current flow between the cath-` ode and the anode of tube T3, thusproducing a small voltage drop. This voltage drop is applied to the grids of tubes 2 and 3 of the conventional,"

receiving set and serves to provide a high negative bias which willv cut oiT the anode current in theseY tubes and thereby ,effectively4 preventrsaid tubes from acting as radio frequencyamplifiers in the radio frequency portion of the said conventional receiving set. y

The lead wire from the tuning coil L2 to. condenser Cswhich is in series in the circuit, and from the condenser Cs ltothe grid oftube Ta,

obtained in this manner.

Re is a highY resistance connected from the plate "When no signal is being received on the auX- iliary receiver, the interrupter unit is not in operation, but because resistor R5 (which is connected to resistor Re and to the plate of tube T3) Vis`grounded to the chassis, a normal grid-bias voltage is allowed to flow through said resistor.

lThis bias voltage (approximately 2.5 volts) may be obtained from the conventional broadcast receiver in the manner` specified and usual to all conventional broadcast circuits and is preferably Between the cathode of Vany detector or amplifier tube, of the type of Ytube T3', and the ground (chassis) is inserted a resistor, the value of the resistance being determined by the tube characteristic. thisV resistor, which is negative, is connected to the ground (chassis) and will permit the cathode to become positive. 'I'his is due to the current owing through the tube, the grid of this tube being connected to a coil which is connected to the ground (chassis) by means of a wire leading to the chassis of the receiving set, or else the said coil may be connected to a resistor, which is connected to the ground (chassis), so that the ground will then become negative with respect to the cathode of the same tube. The above explains the term negative bias.

The voltage action between the grid and plate output of tube T3 results in the complete and instantaneous interruption of the receiving set on regular broadcast signals and allows the receiving set tofunction on another signal of a different frequency which is being received through the interrupter unit, such voltage action further causing the receiver automatically and instantly to resume operation on the original signal when the signal to the interrupter unit ceases.

R4 is a high negative bias control resistor for One side of the grid of tube T3 while R6 and R10 are ad- Y justable bleeder resistors, and R9 is a voltage drop resistor.

C10 and C11 are high capacity by-pass condensers to act as a direct radio frequency short circuit between condensers Ca and Cb to tune coils La and Lb of the receiving set.

The filament or heater leads Y from the tubes of the interrupter unit are connected to the Y leads of the receiving set which is of conventional circuit and for that reason is not here described in particular detail except insofar as the interrupter unit is connected to it.

The condensers C1 and C2 are semi-adjustable and are initially tuned and set to the desired frequency for operation of the interrupter.

It is to be understood that although in its preferred form our invention includes an interrupter unit responsive to short wave signals such unit may, within the purview of the invention, be responsive to any wave length, either short or long, utilizing any frequency band. Further, the interrupter circuit shown is merely by way of illustration, and may, instead, be adapted for long distance reception by the addition of radio :frequency or intermediate frequency amplification stages.

i From the foregoing it will be apparent that 1 our invention provides an efficient and compact but inexpensive means for automatically receiving signals of different frequency from that of the receiving set to ywhich it is connected, and Without necessitating the use of a separate antenna system, such means functioning automatically to block the signals of one frequency while those of a selected different frequency are being received and translated into sound, and further functioning automatically to resume the audible reception of the signals of the one selected frequency when those of the other selected frequency have ceased. The center tap of the power transformer is negative with relation to the ground (chassis) due to the resistor Ra. The difference in voltage depends upon the current drawn through the resistor Ra and on the resistance ofthe said resistor.

What We claim is:

1. In combination wtih an antenna and a receiver connected thereto, responsive to signals of a selected frequency and comprising radio frequency and audio frequency stages, a second receiver circuit responsive to a predetermined signal of different frequency and also connected to said antenna, a control tube in said second receiver circuit, said control tube having a grid, a cathode and an anode, means normally impressing on said grid a potential negative with respect to the cathode and means whereby the negative potential of the said grid is removed when said second receiver is fed with such predetermined signal energy of different frequency, whereby electron flow from the cathode to the anode of said control tube takes place, thus providing an output of current from the said anode, and connections for applying a negative bias derived from the anode current of said control tube to the grids of the radio frequency tubes of the first receiver, thereby automatically blocking the electron flow in such radio frequency tubes and interrupting the audible reception of the signals to which the first receiver is responsive, during the reception of signals of the selected frequency to which the second receiver circuit is tuned.

2. In combination with an antenna and a receiver connected thereto, responsive to relatively long wave length signals and comprising radio frequency and audio frequency stages, a second receiver circuit responsive to a predetermined relatively short wave length signal and also connected to said antenna, a control tube in said second. receiver circuit having cathode, grid and anode electrodes, means for normally maintaining said grid negative With respect to said cathode, means for providing a positive voltage on the said grid responsive to passage of a signal through the said second receiver circuit, thereby establishing a relatively large anode-cathode current in said tube, means including a resistance traversed by such current whereby a voltage drop is provided, and means for applying such voltage drop as a negative bias to the grids of the radio frequency tubes of the first receiver, to temporarily prevent such tubes from amplifying, so as to interrupt the audible reception of the long wave length signals during reception of the selected short wave length signals, and a detector tube in said second receiver circuit, the anode lead of which is connected with the anode lead of the first audio stage in said first-named receiver to electrodes and connected in circuit with one of y said receivers and having an anode connected to at least one of the grids of the radio frequency Y ampliiier tubes of said other receiver, means for applying a voltage on the grid of said control tube produced by and in response to a signal impressed upon the circuit containing such tube, and thus controlling the action of said radio frequency ampliiier tubes through their said connection with the anode of said control tube, whereby when a signal is received by the circuit containing the control tube, audible reception by said other receiver will be interrupted.

4. The combination of two radio receivers tuned to be responsive to signals of different radio frequencies, each receiver including tubes having cathode, anode and grid electrodes, certain of said tubes acting as radio frequency amplifiers, an antenna common tosaid receivers, a control tube having cathode, anode and grid electrodes and connected in` circuit with one of said receivers and having an anode connected to at least one of the grids of the radio 'frequency amplifier tubes of said other receiver, means for applying a voltage on the grid of said control tube produced by and in response to a signal impressed 'upon the receiver with which the control tube is in circuit, thereby to produce a gridblocking voltage output from the anode current of said control tube which, being applied through said connection to at least one of the grids of said radio frequency amplifier tubes, interrupts the audible reception of said other receiver.

5. The combination of a plurality of radio receivers tuned to be selectively responsive to signals of different radio frequencies, an antenna common to all of said receivers, a control tube in circuit with one of said receivers and having a grid which is normally maintained at a negative potential with respect to the cathode, but which, when a signal of proper frequency is impressed upon such circuit, produces a corresponding variation of effective impedance of the control tube whereby a pulsating rectied anode current is provided, means to produce a voltage drop from said current, connections between the anode of such tube and the grids of the radio frequency tubes of another receiver, thereby to interrupt the electron iiow in said radio frequency tubes and, consequently, to interrupt audible reception through such receiver, by applying said voltage drop as a grid-blocking negative bias on the grids of such tubes through said connections when the anode current in said control tube is increased by the impression of a radio frequency signal upon the circuit in which the control tube is connected, together with an audio amplification system common to all of said receivers.

6. The process of controlling the operation of a first radio receiving set by a second, which consists in tuning the first set to a Wave length of signals which are substantially continuously available, whereby said set normally produces an audible response corresponidng to said signals, tuning the second set to a wave length of signalmodulated carrier Wave signals Whicliare available only at relatively, infrequent intervals, causing said second set to produce an Vaudible response corresponding to said relatively infrequent signals, and at the same time causing the second setto produce a. unidirectional voltage upon receipt of said signals, and applying said Voltage as a blocking bias in the rst set, to interrupt the production of audible response to the continuously available signals thereby, during such infrequent periods of activity of the second set, whereby the second set alone then produces audible sounds.

RALPH D. WICHMAN, JR. ROBERT T. MCCLELLAN. 

